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| Home > Publications database > Untersuchugnen zur physikochemischen Wechselwirkung organischer Polysäuren mit Oxiden |
| Book/Report | FZJ-2019-00818 |
1998
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/21405
Report No.: Juel-3570
Abstract: The thesis presents results concerning the adsorbate structure and the adsorption mechanism of the polyelectrolytes polyacrylic acid, polymethacrylic acid and humic acid onto the oxides gibbsite, goethite and alumina. The main focus is set an the influence of different parameters such as ionic strength, divalent cations and molar mass of the poiyacids an the adsorbate structure. Based an this results the interaction of the cationic surfactant cetylpyridinium chloride and of 2,4-dichlorophenol respectively is examined. The observed adsorption isotherms of every polyacid show all die saure high affinity type being typical for polymer adsorption. The maximum adsorbed amount is correlated linearly with the proton charge density 0H of the oxides in the low ionic strength of 0.01 M NaCl. During the adsorption process the surface charge of the oxides rums from positive to negative. Low amount of polyelectrolyte destabilize the suspension and, only when the oxide surface is covered totally, the suspension is stabilized again. An increase of the ionic strength or the addition divalent cations cause a rise of the maximum adsorbed amount of polyacid. Due to higher ionic strength or divalent cations the repulsion of the negative charged polyelectrolyte segments is reduced. Therefore loops and tails in the adsorption layer are stabilized. Additionally the increase of the maximum adsorbed amount with the ionic strength indicates a chernical bond between polyacid and surface. The results of calorimetric experiments assure this conclusion. Independent of the molar mass polyacrylic acid adsorbs in a flat conformation, if the ionic strength is low. Above a certain threshold of the ionic strength higher molar masses are better adsorbed than lower ones. Under these conditions the polyacrylic acid adsorbs in a coiled conformation. Results obtained from iR spectra imply that the polyacids are bound to die Alumina surface bya ligand exchange mechanism. Polymethacrylic acid and polyacrylic acid form a bidental bridging complex. However for the humic acid it is difficult to identify die surface complex by IR spectra. The spectra confirm the conclusions of die calorimetric experiments. Polyacrylic and polymethacrylic acid adsorb in a flat conformation with low adsorbed amounts and in a coiled conformation with increasing adsorbed amounts. With polyacrylic acids the part of carboxylic groups bound as trains to the surface is always greater compared to polymethacrylic acid. Cetylpyridinium chloride does not adsorb on pure goethite, gibbsite and alumina. But the surfactant is bound onto an oxide surface modified with polyelectrolyte. During the adsorption the surface charge of the modified surfaces changes from negative to positive. Oxides modified with the same polyelectrolyte show the same adsorption isotheiin . So the type of the polyelectrolyte determines the adsorption properties of the modified oxide. Very low amounts of die non-ionic 2,4-dichlorophenol are bound to pure alumina modified with polyacrylic or polymethacrylic acid. In contrast to this the amount of adsorbed 2,4-dichlorophenol increases, if the surface is modified with humic acid due to the hydrophobic parts of die humic acid. The importance of hydrophobic parts is emphasised by the high adsorbed amount of 2,4-dichlorophenol on alumina modified with Sodiumdodecylsulphate.
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